The consumer who grabs the half-gallon of organic milk instead of regular milk knows something about the cost of “going green.” It’s high.

A recent study by the U.S. Department of Agriculture spells it out. Nationally, organic milk cost 98% more than regular milk in 2004: $4.01 for organic, $2.02 for regular, a price difference of $1.99. That’s almost enough to buy another half-gallon of regular milk.

Prices of organic produce, poultry and eggs are also higher, far more than 200% higher in the case of poultry, according to the USDA. But green-minded consumers — who care about their health, as well as “green” issues like global warming, pollution and loss of wildlife — are also in the market for natural cleaning products, sustainably crafted furniture and hybrid cars, a rapidly growing marketplace of products that almost always cost more than their conventional counterparts.

Take the “giddy-up short sleeve shirt” for women by Nau, a new clothing company in Portland, Ore. Made out of organic cotton poplin and a little spandex, the tailored shirt, with a curved hem and snaps up the front, sells for $95. Yikes!

So what’s a consumer who is on a budget but wants to “go green” supposed to do? Below are two steps that will make the job a lot easier:

1. Think about why you are buying green in the first place

A consumer worried about global warming may consider buying a hybrid car, which can get 50 miles to the gallon. Hybrid cars, however, tend to cost more: The manufacturer’s suggested retail price of the 2007 Honda Civic Hybrid is $22,600, 51% more than lowest-priced Honda Civic Sedan.

For the green consumer on a budget, a better choice would be to hang on to the old car and drive it less. “You can come out with same amount of fuel savings over the course of a year if you can find ways to not drive your car — get on your bike, walk,” says Seth Bauer, editorial director of The Green Guide, an online consumer resource.

Buying less and wasting less is the easiest, cheapest way to show concern for the environment. “The simplest thing you can do is not waste as much as we all do right and left in our daily lives,” Bauer says. “The fundamental question is, what don’t you need?”

Many consumers turn to “green” products like laundry detergents and household cleaners for their health, often because they are allergic to perfumes or chemical additives. But making laundry detergents out of natural instead of synthetic materials costs more, says John Murphy, senior vice president of sales for Seventh Generation, which makes “nontoxic and environmentally safe” household products. “The conventional brands just don’t go through the same level of diligence we do around scent and surfactants,” Murphy says.

Seventh Generation products also cost more because retailers use the larger profit margins on the company’s products to offset thinner margins on better-known brands. The company is working with some retailers to learn the “optimum price point” for drawing in the green customer.

2. Think about purchases and actions that give the most bang for the buck

Some easy suggestions are to wash clothes in cold water, pull the plug on TVs and VCRs when they aren’t in use, weatherstrip and caulk windows and doors, and switch to compact fluorescent light bulbs, which are three or four times as efficient as incandescent bulbs, according to the “Consumer’s Guide.” CFLs can cost more upfront — perhaps up to $2.50 a bulb instead of 50 cents — but they last longer. “The cost-effectiveness of them is so great that if you’re on a budget, there is even more reason to do it,” Leon says.

Buying organic food can have a big, positive effect on the environment as well by reducing pesticides and fertilizers that harm soil, waterways, and wildlife. But organic food does cost more. Leon’s suggestion is to make an organic budget. “Say it’s $1 a week — and nothing more — then what I would do is say, ‘How do I get the most out of that dollar?’ ”

The budget organic can take two approaches: buy organic when the price is right (i.e. not too much higher than conventional) or buy organic when the conventional choice tends to retain pesticide residue. Produce with high pesticide residues includes apples, cherries, grapes, peaches, strawberries, celery, green beans, lettuce and winter squash, Leon says.

The high price of organic food stems largely from supply and demand economics: There’s more demand than supply, so prices are higher. With organic milk, the supply is beginning to increase a little, but not enough to make a dent in the price, says Carolyn Dimitri, an economist with the USDA’s Economic Research Service and co-author of “Retail and Consumer Aspects of the Organic Milk Market,” published in May.

Organic food can also cost more because the costs of production are higher. Up to 70% of the cost of raising organic chickens is the special feed, which costs 50% to 100% more than conventional feed grain, according to a December 2006 report from the USDA’s Economic Research Service. Organic poultry flocks also tend to be smaller, have a higher mortality rate and require a longer production cycle, the report says.

Some economists argue the true costs of conventional food are not reflected in the price consumers pay. The negative effects of conventional agricultural production on water, soil, air, wildlife and humans total $5.7 billion to $16.9 billion a year, economists Erin M. Tegtmeier and Michael D. Duffy of Iowa State University concluded in a 2004 study published in the International Journal of Agricultural Sustainability. The study shows “consumers pay for food well beyond the grocery store checkout” in higher utility bills, taxes and in declining environmental and personal health.

Such “hidden” costs are part of the reason why advocates for green buying practices argue consumers need to rethink their consumption patterns and focus less on the cost of individual items.

Buy green by buying less often

That, in fact, is what Nau is trying to do with its outdoor apparel. From the start, the company’s creators thought about the criteria for the “ideal garment.” One of those criteria is durability.

Nau expects its clothes to last through 10 years of wear and tear and changing fashion, says Ian Yolles, Nau’s vice president of brand communication. A Nau jacket may cost $180, but in the long run, it’s cheaper than buying three less-expensive jackets that fall apart or go out of style.

“You can buy a piece of apparel, and if it isn’t constructed in a way that will ensure it will last over a long period of time, it’s not particularly sustainable,” Yolles says. Still, Yolles admits, Nau’s approach requires some re-education.